This invention relates to an optical disc recording device for recording information on an optical disc and, more particularly, to an optical disc recording device capable of recording information easily on an optical disc regardless of difference in the type of an optical disc caused by difference in a recording material used for the optical disc or other factor.
There is a recordable optical disc called a CD-WO disc (write once type disc of the CD format) which is used for recording various information including music information.
A material selected from various materials is used for forming a recording layer of a CD-WO disc. One of these materials is a dyestuff. A recording power (power of laser beam required for recording, i.e., recording sensitivity) differs depending upon the type of dyestuff. On the other hand, it is required for a recording device to perform recording of information on a disc always in an optimum recording state no matter how the material of the recording layer is different and, therefore, parameters including the recording power (generally referred to as "write strategy") need to be adjusted depending upon the type of an optical disc used.
In a prior art recording device, a test writing is made by using a portion which is inner of a lead-in area of an optical disc on which information is to be recorded, the recorded information is reproduced and a recording power at a time point when the best reproduced signal is obtained is selected, and this selected recording power is determined as one to be used for actual recording. The test writing is made, for example, by recording a test pattern consisting of a combination of 11T-11T and 3T-3T while changing the recording power gradually by a 0.3 mW to 0.5 mW step. Then, this recorded test pattern is reproduced and asymmetry (a parameter for assessing the quality of a recorded signal) is obtained from the reproduced waveform of 11T-11T and 3T-3T for each recording power. A recording power at a time point when a desired asymmetry has been obtained is selected and the recording power used for actual recording is determined at this recording power.
In the above described optical disc recording device in which a recording power is determined by test writing, it is rather troublesome to determine the recording power. Particularly, in a case where there is a parameter other than the recording power which must be adjusted (e.g., amounts of shifting of timings of starting and ending recording of a signal to be recorded and an amount of correction of laser beam projection time etc.), it is extremely difficult for a user to set an optimum state by the test writing.
It is, therefore, a first object of the invention to provide an optical disc recording device capable of recording information on an optical disc easily regardless of difference in the type of the optical disc.
In the CD-WO format, the recording pit length of 3T to 11T (1T=4.3218 MHz=231 ns) is employed. If, however, laser beam of a pulse width which is equal to a pit length of a pit to be formed is used, a pit which is actually formed will be of a pit length which is larger by about 1T than the pit length of the pit to be formed due to heating of the recording material. For preventing this excessive pit length, so-called (n-1) strategy is employed. According to this (n-1) strategy, as shown in FIG. 5, a recording laser beam of a pulse width (n-1)T+.alpha.(nT) which is shorter by about 1T than the pit length of a pit to be formed is projected. When, for example, a pit of a pit length of 3T is to be formed, a recording laser beam having a pulse width of 2T+30 ns to 70 ns is used. When a pit of a pit length of 4T is to be formed, a recording laser beam having a pulse width of 3T+20 ns to 40 ns is used. When a pit of a pit length of 5T to 10T is to be formed, a recording laser beam having a pulse width of 4T is used.
For a CD-WO disc, K-factor is used as an index representing an amount of deviation of pit length of an actually formed pit from pit length of a pit to be formed K-factor is determined in the following manner: ##EQU1##
K-factor is required to be e.g., 0.8 or below because, when it is too large, a block error tends to be produced in reproduction of a signal. In a cyanine disc, the condition of K-factor being 0.8 or below is satisfied by recording a signal with the above described pulse width of (n-1)T+.alpha.(nT). In a phthalocyanine disc, however, recording with the pulse width of (n-1)T+.alpha.(nT) has resulted in increased pit deviation between (an amount of deviation of the pit length of an actually formed pit from a standard value) as shown in FIG. 6. According to the standard, the pit deviation is required to be within error ranges of .+-.40 ns for 3T and .+-.60 ns for 11T. Pit deviation in the phthalocyanine disc however exceeded these error ranges for 3T and 7T to 11T. For this reason, as shown in FIG. 8, there is likelihood of increase in K-factor with resulting occurrence of a block error.
For reducing K-factor, it is necessary, as shown in FIG. 7, to reduce recording power. For reducing K-factor to a value below 0.8, it is necessary to perform recording with a recording power which is smaller than one within an optimum power range necessary for recording. If, however, recording is made with a recording power smaller than one within an optimum power range, it becomes difficult to form an accurate pit and, as a result, the quality of a signal recorded is deteriorated and the rate of occurrence of error in reproduction increases. Accordingly, when recording is made in a phthalocyanine disc by using the recording laser beam projection time of (n-1)T+.alpha.(nT), it is not possible to reduce deviation in pit length of an actually formed pit from a standard pit length while preventing deterioration in the quality of a recorded signal.
It is, therefore, a second object of the invention to provide an optical disc recording device which, in recording a signal on a phthalocyanine optical disc, is capable of reducing an amount of deviation of a pit length of an actually formed pit from a standard value while preventing deterioration in the quality of a recorded signal.